1. Field of the Invention
The present provisional application relates to flash memory technology, and more particularly to flash memory suitable for high density implementations.
2. Description of Related Art
Nonvolatile memory is computer memory that can retain the stored information when it is not powered. Nonvolatile memory includes flash memory. Flash memory applications can include code flash memory applications or data flash memory applications. Code flash memory applications typically involve frequent read operations but infrequent update operations. In comparison, data flash memory applications typically involve infrequent read operations but frequent update operations.
Data flash memory often is used for mass storage applications, in which a majority of the program, erase and read transactions involve patterns of data usage involving relatively large data sets. Code flash memory is often used for storage of data like computer instructions, in which a majority of the program, erase and read transactions involve patterns of data usage involving relatively small data sets, like updates to instructions and subroutine segments within computer programs and setting and changing values in parameter sets.
In general, data flash and code flash are differentiated by operation algorithms for programming, erasing and reading the data, and by the memory cell structures which are adapted to the operation algorithms. Integration of conventional flash memory technology for both code and data flash purposes into a single chip can be done with multiple arrays having different memory cell structures, one for code flash and one for data flash, to serve these functions. This approach requires different memory cell structures on a single chip and complex operation algorithms adapted to the different structures. Another approach is to have the same memory cell structure for both code and data purposes, and vary bias conditions on memory cells of the same structure to meet requirements for the different purposes. One issue with the latter approach is that code flash memory applications require better read disturbance immunity than data flash memory applications to avoid code corruption.
It is desirable to provide improved read disturbance immunity in a section of the memory on the chip for the code flash memory applications.